Thin film transistors have been regarded as excellent transducers for highly sensitive and disposable biosensors. Sensors based on organic thin film transistors (OTFT) have attracted much attention recently for its easy fabrication and low cost. Organic electrochemical transistors (OECT), are an interesting class of OTFT, and have been extensively studied for the applications of sensors due to their low operating voltages, simplified structure, and the ability to operate in aqueous environments that are essential for biological applications. The first OECT based on polypyrrole was reported in 1984 which was a new direction in the field of OTFTs. Since then, OECTs based on several different conducting polymers were investigated and have shown broad applications of chemical and biological sensing, including humidity sensors, pH and ion sensors, glucose sensors, and cell-based biosensors. The conducting polymer PEDOT:PSS has very important applications in organic electronic devices, including organic solar cells, organic light emission diodes and OTFTs, due to its high conductivity and solution processibility. Recently, PEDOT:PSS has been successfully used as the active layer of OECTs and such devices have shown excellent performance in various applications especially for biosensors in view of their biocompatibility and stability in aqueous environments.
A highly sensitive glucose sensor is desirable in the diagnosis of diabetes. The application of OECTs based on PEDOT:PSS in glucose sensors has been reported. For these sensors, enzyme (glucose oxidase) and glucose are mixed together in aqueous solutions during the measurement without any surface modification on the gate and the active layer of the OECTs. The detection limit of that type of glucose sensor is about several μM, which is sensitive enough for measuring glucose levels in human saliva. Therefore the application of these devices is for low cost and noninvasive blood glucose monitoring.